Strong Seasonal Variations of Seismic Velocity in Eastern Margin of Tibetan Plateau and Sichuan Basin From Ambient Noise Interferometry

Ambient noise interferometry between seismic stations makes it possible to monitor temporal changes of the Earth's media continuously. Here, we examined seasonal changes of Rayleigh-wave empirical Greens functions at 2–10-s period from 8 years of continuous data of 200 seismic station pairs in Sichuan, China. We used a wavelet decomposition to extract the seasonal signals. We found that most station pairs show seasonal variations with velocity perturbations of up to 0.8%. The seasonality varies in strength, amplitude, phase, periods, and location, but the phase is remarkably consistent, with the largest changes mostly in summer or winter months. We believe that the cause of the seasonality is likely the elastic loading due to regional precipitation. The effect is greater in the tectonically active Tibetan Plateau margin than in the stable Sichuan basin and in the deeper crust than in the uppermost crust. The effect is also strongly influenced by local crustal structure. Our results indicate that studies of tectonic crustal changes need to consider non-tectonic effects.